1. Field of the Invention
The present invention relates to a compact image pickup lens for an image pickup apparatus incorporating a solid-state image sensor, such as a CCD type image sensor and a CMOS type image sensor.
2. Description of the Related Art
In recent years, accompanying the improvement in performance and reduction in size of an image pickup apparatus using a solid-state image sensor, such as a charge coupled device (CCD) type image sensor and a complementary metal oxide semiconductor (CMOS) type image sensor, mobile telephones and portable information terminals including such an image pickup apparatus are spreading. Further, an image pickup lens mounted in such an image pickup apparatus is demanded increasingly for further reduction in size and improvement in performance. As an image pickup lens intended for such a use, there has been proposed an image pickup lens having a configuration of five lenses because of the possibility of improvement in performance compared to a lens having a configuration of three or four lenses.
As an image pickup lens having a configuration of five lenses, an image pickup lens has been disclosed, which is configured by a first lens having a positive power, a second lens having a negative power, a third lens having a positive power, a fourth lens having a negative power, and a fifth lens having a negative power in this order from an object side (for example, Patent Literature 1).
Further, an image pickup lens has been disclosed, which is configured by a first lens having a negative power, a second lens having a positive power, a third lens having a negative power, a fourth lens having a positive power, and a fifth lens having a negative power in this order from the object side (for example, Patent Literature 2).
However, in the image pickup lens described in above Patent Literature 1, the first lens to the third lens contribute to most of the power of the entire system and the fourth lens and the fifth lens have only the effect as an image plane correcting lens having a weak power, and therefore, the image pickup lens has such a problem that aberration correction is insufficient and if the total length of the lens is reduced, it becomes difficult for the image pickup lens to cope with a larger number of pixels in the image sensor because of deterioration in performance.
Further, in the image pickup lens described in above Patent Literature 2, the former group configured by the first lens and the second lens includes a spherical surface system, and therefore, it is not possible to secure excellent performance because of insufficient correction of spherical aberration and comatic aberration. Furthermore, because not only the former group but also the latter group including the third lens and subsequent lenses has a configuration of the positive power, the principal point position of the optical system is on the image side and the back focus is increased compared to a telephoto type configuration in which the latter group has a negative power, and therefore, this is a type disadvantageous in downsizing.    PTL 1: U.S. Patent Publication No. 2007-0229984    PTL 2: U.S. Patent Publication No. 2007-0236811